In processing lines where carton blanks are conveyed along a straight line path for folding and gluing, it is relatively straightforward to engage the leading and lateral edge panels or flaps with plows or shoes or the like and fold them into position for gluing. The trailing panels or flaps of carton blanks are more difficult to engage and fold because the blanks are moving in the direction of the fold and hence away from any folding mechansim. A trailing edge folder for operating with a mechanically timed feed which employs a shaft that is intermittently rotated in conjunction with the timed carton feed is shown in U.S. Pat. No. 3,330,185.
Another device for folding the trailing edges of carton blanks is described in U.S. Pat. No. 3,901,134. An endless loop having a run below the carton blank conveyor is intermittently operative and carries pivotal folding fingers that are biased to a rest position and pivoted by various cams as the finger is carried below the carton blank to engage and fold its trailing end flap. While the mechanism is adjustable to accommodate blanks of various sizes and does not require a mechanically timed feed, its speed in handling small carton blanks is limited by the speed at which successive fingers are carried onto the upper run of the loop, and smaller boxes or cartons may have to be spaced at substantial intervals from each other thereby reducing the efficiency of the apparatus. Additionally, this mechanism, which includes a chain drive, requires a great deal of maintenance, is subject to fast wearing of components, and thus presents significant operational difficulties. Although the speed of the fingers might be adjusted by changing the geometry of the fingers and loop, such changes are cumbersome and such apparatus is generally operated at a constant speed.
A more recent trailing edge folder and controller are shown in commonly-assigned U.S. Pat. Nos. 4,432,745 and 4,539,002, the respective teachings of which are hereby incorporated herein by reference. This trailing edge folder includes an intermittently rotatable shaft mounted below and transverse to the horizontal path of the carton blanks. The shaft includes an arm or arms that extend generally radially from the shaft. The arms have folding heads at their distal ends for contacting and folding the trailing panels of successive blanks along fold lines parallel to the respective trailing edges. The shaft stops and dwells when a respective trailing edge is folded about 180.degree. on the fold line. After the panel is pulled from under a head and the blank is out of the path of the head, the shaft rotates further to a start position until the next blank appears along the path.
More specifically, this trailing edge folder is powered by the main drive of the blank folding machine of which the folder is an accessory. The shaft is connected to a main drive power takeoff using a clutch/brake mechanism. While this trailing edge folder operates satisfactorily, the need continues for improved folders offering greater accuracy, longer life, quieter operation and greater production rates. As the folder shaft is connected to the machine main drive, vibrations occasioned by starting and stopping of the folder shaft are reflected back into the main machine drive. This arrangement also requires that the folder shaft have the same angular velocity throughout its cycle of operation.